This invention relates to powdered metal parts and more particularly to a powdered metal article having a wear resistant coating thereon.
It is known in the art to make parts for various structures and machines by subjecting a powdered metal to heat and pressure to compact it into an essentially solid body which may be of the desired size and shape or may be subsequently machined or otherwise formed into the desired size and shape. Such parts have many advantages in particular applications since a wide range of physical characteristics may be designed into the powdered metal bodies comprising such parts.
In other words, the powdered metal or mixture of powdered metals which are compacted to form the bodies of which such parts are made, can be selected to provide physical characteristics not obtainable through the use of solid alloys of metals. In addition, the mechanical nature of the bodies, since they consist of a mass of powder particles bonded to each other with minute voids therebetween rather than a solid solution of the constituents of the powdered metal particles provide physical characteristics that are highly desirable for certain applications.
Although powdered metal articles exhibit good mechanical strength, they are subject to excessive wear in use and are easily weakened by subjection to excessive heat or temperature gradients. Furthermore, it has been difficult, if not impossible to provide composite powdered metal articles having special surface characteristics different from the remainder of the body since other metals could not be successfully bonded to the surfaces of powdered metal articles.
Attempts to apply fused metallic coating to the surface of powdered metal articles through the use of heat have failed where the melting temperature of the metal to be applied is too high, since the required heat will weaken the powdered metal article and may actually cause it to crumble or fall apart. Where the melting temperature of the metal to be applied is too low, then the resulting surface coating will not have sufficient hot strength to be useful in many of the applications in which powdered metal articles may be used with advantage. Attempts to find a compromise between these two extremes have failed due to the excessive absorption of the coating metal into the volume of the powdered metal article by a capillary action which causes the coating metal to permeate the volume of the body through the voids between the powdered metal particles when the temperature of the body approaches that required to melt the coating metal. Excessive absorption of the coating metal will not only modify the desired physical characteristics of the powdered metal article but will also make it difficult to obtain the desired thickness of surface coating in addition to requiring the use of an excessive amount of coating metal which is often expensive.
It is a general object of this invention to provide a powdered metal article with a wear resistant surface of fused metal which is firmly bonded to the surface of the powdered metal article without excessive penetration into the volume of the powdered metal body.
It is a specific object of this invention to provide an engine valve seat insert comprising a body of pressed, sintered and heat-treated metal alloy powder with a wear-surface of a fused heat resistant alloy bonded thereto.